The invention relates to surface plasmon resonance devices and in particular to application of surface plasma resonance devices to biosensors.
Surface plasmon resonance (SPR) is used to examine the optical properties of a thin film which is under investigation. Surface plasmon resonance has been used, for example, in biosensor apparatus for reading thickness changes in binding processes on microarray biochips. The use of SPR permits these changes to be detected as changes in local optical reflectivity.
SPR is a useful technique because the effect being studied only exists at surfaces, that is, at interfaces between a metal and dielectric materials.
Known SPR devices, comprising a metallic layer and a recognition layer deposited on a prism or waveguide, detect changes in the plasmon resonance angle when an analyte changes the recognition layer""s refractive index.
Known SPR apparatus has certain problems. One problem is that the apparatus implements an SPR technique which is a steady state technique. That is, the apparatus looks for a dark spot in reflectivity by moving a light source or by implementing multiple angles. Known SPR techniques have limited dynamic range and must be operated within limited refractive index values. The fundamental SPR event in known devices also cannot be modulated. Their sensitivity is limited.
The invention is an improvement in SPR apparatus and methods. The invention resides in the inclusion of, for example, an electro-optically active or thermally controlled layer that can be used to xe2x80x9ctunexe2x80x9d the plasmon resonance, to modulate it, or to gate it. The invention is applicable to surface plasmon resonance biosensing by active multilayer detection. Active multilayer devices using the principles of the invention enable the use of SPR techniques in numerous applications, for example, in micro-assays for diagnostics, for drug development or for biotechnology experiments, by enhancing sensitivity and range of operation while simultaneously shrinking the size requirements of SPR devices. Other controlled layers may be any such layer the refractive index of which can be controlled.